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Glycemic Index (extracts)

Extracted the following information from Low GI guide to Diabetes

BY: Dr Jennie Brand-Miller, Kaye Foster-Powell with Johanna Burani

Introduction to Glycemic Index

The glycemic index is a useful tool which may have a broad spectrum of applications, from the maintenance of fuel supply during exercise to the control of blood glucose levels in diabetes. .. – James Hill PhD, Director, Center for Human Nutrition, University of Colorado Health Sciences Center

The glycemic index is a ranking of foods based on their immediate effect on blood sugar levels. Carbohydrate foods that break down quickly during digestion have the highest GI values because their blood sugar response is fast and high. Carbohydrate foods that break down slowly, releasing glucose gradually into the bloodstream, have low GI values.

Research on the glycemic index has turned some widely held beliefs upside down. The surprises:

Many starchy foods (some types of bread and potato and many types of rice) are digested and absorbed very quickly – not slowly as we had always assumed.

Moderate amounts of many sugary foods did not produce the dramatic rises in blood sugar that we had thought.

Insulin

The pancreas is a vital organ near the stomach, and its main job is to produce the hormone insulin. Carbohydrate stimulates the secretion of insulin more than any other component of food. The slow absorption of the carbohydrate in our food means that the pancreas doesn’t have to work so hard and needs to produce less insulin.

If the pancreas is overstimulated over a long period of time, it may become “exhausted” and type 2 diabetes can develop in genetically susceptible people. Even without diabetes, high insulin levels are undesirable because they increase the risk of heart disease.

Insulin influences the way we metabolize foods, determining whether we burn fat or carbohydrate to meet our energy needs, and ultimately determining whether we store fat in our bodies.

Some researchers think that high insulin levels might cause the muscle in the walls of blood vessels to thicken. This thickening would cause the blood vessels to narrow and slow the flow of blood.

With low-GI foods, there’s a reduced secretion of the hormone insulin over the course of the day. With high-GI foods, the body produces larger amounts of insulin, resulting in higher levels of insulin in the blood.

Carbohydrate

Carbohydrate is the starchy part of foods such as rice, bread, potatoes, and pasta. It is also the essential ingredient of sweet foods: The sugars in fruit and honey are carbohydrates as are the refined sugars in soft drinks and confectionary. Carbohydrate mainly comes from plant foods, such as grains, fruits, vegetables, and legumes (peas and beans). Milk products also contain carbohydrate in the form of milk sugar or lactose.

Some foods contain a large amount of carbohydrate (such as cereals, potatoes, and legumes), while other foods are very dilute sources, such as carrots, broccoli, and salad vegetables. Foods high in carbohydrate include:

There are still people who think that because carbohydrate raises blood sugar, people who have diabetes should not eat it at all. This is wrong: Carbohydrate is a necessary part of a healthy diet. For people with diabetes, choosing carbohydrate foods with a low glycemic index flattens out the peaks and valleys in blood sugar and helps achieve more stable blood sugar levels.

Our bodies burn fuel all the time, and the fuel our bodies like best is carbohydrate. Carbohydrate is the only fuel the brain and red blood cells can use, and the main source of energy for the muscles during strenuous exercise. Carbohydrate is a vital energy source and you can’t afford to leave it out. Carbohydrates, however, were not created equal – you must choose the right kind of carbohydrate for your lifestyle.

What’s wrong with a low carbohydrate diet?

There is little scientific evidence to back up or refute low-carbohydrate diets. One reason for the popularity of low-carbohydrate diets for weight loss is that initial loss is rapid. Within the first few days, the scales will be reading 4-7 pounds lower. That’s really encouraging sign to anyone trying to lose weight. The trouble is that most of that weight loss isn’t body fat, but muscle glycogen and water.

When carbohydrate is no longer being supplied in sufficient amounts by your diet, the body uses its small carbohydrate reserves (muscle glycogen) to fuel muscle contraction. One gram of carbohydrate in the form of muscle and liver glycogen binds four grams of water. So when you use up your total reserves of 500 grams of glycogen within the first few days, you also lose 4 pounds of water, for a total loss of 5 ½ pounds, none of it fat. Conversely, when you return to normal eating, the carbohydrate reserves will be rapidly replenished along with water, which is why there is an instant weight gain.

People who have followed low-carbohydrate diets for any length of time observe that the rate of weight loss plateaus off and they begin to feel rather tired and lethargic. That’s not surprising because the muscles have little in the way of glycogen stores.

Key factors that influences the Glycemic Index

Cooking methods
Cooking and processing increases the glycemic index of a food because it increases the swelling of the starch molecules in the food. Rice is one example.

Physical form of the food
An intact fibrous coat, such as that on whole grains and legumes, act as a physical barrier and slows down digestion, lowering a food’s GI value. Beans, barley and whole grain pumpernickel are examples.

Type of starch
There are two types of starch in foods, amylose and amylopectin. The more amylose starch a food contains, the lower the glycemic index.

Particle size
The smaller the particle size, the easier it is for water and enzymes to penetrate. This is why enriched wheat flour (which is a highly processed finely milled flour) has a high GI value, while stone-ground flour with larger particles, has a lower GI value.

Fiber
Viscous, soluble fibers, such as those found in rolled oats and apples, slow down digestion and lower a food’s glycemic index.

Sugar
The presence of sugar, as well as the type of sugar will influence a food’s glycemic index. Fruit with a low glycemic index, such as apples and oranges, are high in fructose. The presence of sugar also will restrict gelatinization (or swelling) of starch that is also present in a food by binding with the water in the food. So some cookies and breakfast cereals that contain sugar may have relatively low GI values.

Acidity
Acids in foods slow down stomach emptying, thereby slowing the rate at which starch can be digested. Vinegar, lemon juice, lime juice, salad dressings, pickled vegetables, and sourdough bread are good examples.

Fat
Fat slows down the rate of stomach emptying, thereby slowing the digestion of the starch. For example, potato chips have a lower GI value than boiled potatoes.

Low-GI Eating

Low-GI eating means making a move back to the high carbohydrate foods that are staple in many parts of the world, especially whole grains (barley, oats, dried peas, and beans) in combination with breads, pasta, vegetables, fruits, and certain types of rice.

The glycemic index is especially important when you eat carbohydrate by itself and not as part of a mixed meal, because carbohydrate tends to have a stronger effect on our blood sugar level when it is eaten alone.

When choosing a between-meal bite, pick a low-fat snack with a low glycemic index. For example, an apple with a glycemic index of 38 is better than a slice of white bread with a glycemic index of around 70, because it will cause a smaller jump in blood sugar levels and quiet the stomach growls until the next meal.

Some snack foods with a very low glycemic index (such as peanuts, at 14) have very high fat content. As an occasional snack they are fine, especially because their fat is heart-healthy. Just don’t go overboard. Seven nuts is a healthy portion – it may seem very small at first, but you’ll soon find the sustaining power in these energy-filled snack choices.

Five Snacking Tips

It is important to include at least two servings of dairy foods each day for your calcium needs. A low-fat milkshake, one or two scoops of low-fat ice cream or yogurt, fat free cooked pudding, or reduced-fat cheese can boost your daily calcium intake.

If you like whole grain breads, an extra slice makes a very good choice for a snack. Other snacks can include toasted sourdough English muffin halves, a whole grain waffle or a slice of raisin bread with a little butter, peanut butter, or apple butter.

Fruit is always a low caloric option for snacks. You should try to consume at least three servings a day. It may be helpful to prepare fruit in advance to make it accessible for quick and easy eating.

Whole grain crackers are a low calorie snack if you want something dry and crunching. Popcorn, sourdough pretzel nuggets, or a small handful of dry- roasted nuts are other good alternatives.

Keep vegetables (such as celery and carrot sticks, baby tomatoes, florets of blanched cauliflower or broccoli) readily available for quick and easy snacking.

Traditional diets all around the world contained slowly digested and absorbed carbohydrate – low-GI foods. In contrast, modern diets with their quickly digested fine white flours are based on high-GI foods.

For once, health experts agree almost unanimously. The food we eat for breakfast, lunch and dinner, and for those in-between snacks, should be low in fat and high in carbohydrate. The same diet that helps prevent our becoming overweight also reduces our risk of developing heart disease, diabetes and many type of cancer.

But the story doesn’t end there. To reduce the fat content of our diet, we need to eat more carbohydrate. In fact, carbohydrate should be the main source of calories in our food – not fat. Carbohydrate and fat have a reciprocal relationship in our diets: If we eat more high-carbohydrate foods, they tend to displace the high fat foods from our diet.